1. Field of the Invention
The present invention relates to a control device of an internal combustion engine having an atmospheric pressure estimation portion applied to a calculation of a control parameter of the internal combustion engine.
2. Background Art
An engine control method called torque-based control is becoming popular recently. According to this method, an output shaft torque of an internal combustion engine (hereinafter, referred to also simply as the engine) is used as a required value of a drive force from a driver or a vehicle side and a generated torque of the engine is controlled using the output shaft torque as an index. Under the torque-based control as above, a target torque of the engine is determined on the basis of an operation amount on an accelerator pedal by the driver. Then, a throttle opening is controlled so that a target intake air flow rate with which the target torque can be generated is sucked into the engine, and an engine output is controlled to be at the target torque by controlling a fuel injection amount and ignition timing according to an actual intake air flow rate. Travelling performance required by the driver is thus achieved.
In order to achieve a target intake air flow rate corresponding to the target torque of the engine as above, an actuator control portion is proposed for an engine control device controlling a throttle opening by driving an actuator continuously provided to the engine throttle. This control portion finds a target opening area of the throttle by calculating a formula of flow rate computation of a restriction flowmeter based on a target intake air flow rate, a pressure ratio before and after the throttle, an opening area of the throttle, and so on. Then, this control portion controls the actuator continuously provided to the throttle so that the throttle has a throttle opening with which the target opening area of the throttle found as above is achieved. However, in order to calculate a throttle opening to achieve the target intake air flow rate by calculating a formula of flow rate computation of a restriction flowmeter, physical quantities before and after the throttle, such as an atmospheric pressure, an internal pressure of an intake pipe (hereinafter, referred to as the intake manifold pressure), and an intake air temperature, are necessary. Accordingly, it becomes necessary to attach sensors detecting these physical quantities. Because the cost is increased by attaching these sensors, there is proposed a method of estimating an atmospheric pressure without using an atmospheric pressure sensor among the necessary sensors.
As a method of estimating an atmospheric pressure without using an atmospheric pressure sensor as above, for example, JP-58-65950 A discloses a method, according to which when throttle openings at a start-up and while the vehicle is moving are equal to or larger than a predetermined value, a value obtained by correcting the intake manifold pressure is used as an atmospheric pressure estimated value. This method, however, has a problem that the throttle opening fails to reach or exceed the predetermined value in some cases depending on an operation state of the driver and the atmospheric pressure estimated value estimated at the start-up is not updated. As a method of solving this problem, there is proposed a method of finding an intake amount from an effective opening area found from the throttle opening and the atmospheric pressure estimated value, and adjusting the atmospheric pressure estimated value so that the intake amount thus found and the target intake amount coincide with each other as is disclosed, for example, in JP 5462390 B. This method can broaden an operation region across which the atmospheric pressure can be estimated in comparison with JP-58-65950 A.
When there is an error in a relation of the throttle opening and the effective opening area due to a variation in throttle machine difference, control can be performed using a throttle opening corrected using a method of having a relation of the throttle opening and the effective opening area be learned as is disclosed, for example, in JP-2008-57339 A.
However, in the case of JP 5462390 B describing the method of finding an intake amount from the effective opening area found from the throttle opening and the atmospheric pressure estimated value and adjusting the atmospheric pressure estimated value so that the intake amount thus found and the target intake amount coincide with each other, when there is an error in the relation of the throttle opening and the effective opening area due to a variation in throttle machine difference, this error is reflected on the atmospheric pressure estimated value and becomes an error from the actual atmospheric pressure. The method disclosed in JP-2008-57339 A to have a relation of the throttle opening and the effective opening area for a variation in throttle machine difference be learned may be applied to the method of adjusting the atmospheric pressure estimated value as above. However, a concrete method of such application is neither described nor suggested. Hence, there is a problem that an exact atmospheric pressure cannot be estimated.